The present invention generally relates to connecting chips or dies to substrates, and, particularly, electrically connecting and bonding the back-side of a die directly to a substrate and protecting conductive traces from contaminants in semiconductor and thermal inkjet printer applications.
One of ordinary skill in the art in semiconductor technology readily understands that integrated circuits (ICs) are formed in and on wafers made from semiconductor material(s) as one of the basic steps of microchip fabrication. The area on a wafer occupied by a discrete IC is called a chip or a die. In the wafer fabrication process, the discrete ICs are formed in and on the wafer surface and are wired together. The resulting circuit is protected with a final sealing layer. Following wafer fabrication, the chips on the wafer are complete, but in untested wafer form.
To use a chip for its intended purpose, such as part of an electronic circuit or electronic product, the chip is packaged in a usable form that provides a lead system to connect the chip to a circuit board or directly to an electronic device. Moreover, the package provides physical protection for the fragile chip, including environmental protection and heat dissipation. An example of a packaged chip 2 is shown in Prior Art FIG. 1.
In the packaging process, the wafer is separated into individual chips or dies through sawing, etching, or scribing. The die needs to be electrically connected and bonded to its substrate prior to packaging and use. This has been accomplished by using an adhesive, such as a gold/silicon eutectic or an epoxy adhesive, to attach the die to the substrate. Electrical connections are then made on the front-side of the die, such as the individual wire bonding shown in Prior Art FIG. 2, where up to hundreds of thin wires 4 (only one shown) electrically connect a interconnect pad 6 on the front-side 10 of chip 2 to a lead 8 on a substrate or package 12 (shown in FIG. 1). The individual wires are expensive and fragile. Moreover, the profile height is relatively high compared to other bonding techniques, which makes this method undesirable for small/shallow package applications.
Another known means for electrically connecting a die to a substrate is via a flip-chip/bump process. This is best seen in FIGS. 3 and 4, where a metal bump 14 is deposited on each bonding pad on the front-side 10 of chip 2 in lieu of wires. The chip 2 is connected to the substrate 16 by flipping the chip 2 over and soldering the bumps 14 to corresponding substrate inner leads 18. This technique has a lower profile than the wire bonding, but is still not ideal for many applications, and, particularly, in corrosive applications.
Referring to Prior Art FIG. 5, another well-known means for electrically connecting a die to a substrate, and most popular in thermal inkjet printhead applications, is the TAB (tape automated bonding) technique. TAB uses flexible continuous tape 20 containing many individual lead systems on the tape. The bond is complete when heat and pressure (such as from a thermode shown at 22) is applied to the tape 20 to physically and electrically bond the inner leads onto the interconnect pads or bonding pads 24 of chip 26. TAB is used extensively in low profile devices. Also, this technique is fast and cost-effective. A major drawback of TAB is the deterioration of the adhesives, and, ultimately, the electrical connections/bonds over time when exposed to corrosive contaminants.
As alluded to above, TAB connections are heavily used in thermal inkjet printer technology because of the low profile that can be obtained with TAB, as well as the speed in which the bonds can be made between the die and substrate during manufacture. Prior Art FIGS. 6-13 are disclosed herein to better educate the reader as to how TAB bonds have been conventionally used in thermal inkjet printers. FIGS. 6-12 are part of the common assignee""s U.S. Pat. No. 5,420,627 (inventors Keefe et al.), granted May 30, 1995, and entitled xe2x80x98Inkjet Printhead.xe2x80x9d
Exemplary of the TAB circuits in thermal inkjet printheads, as can be see in FIG. 9, a printhead 28 comprising a TAB circuit 30 is incorporated into a print cartridge 32. The printhead, or pen, consists of a fluid (ink)-ejecting substrate 34 having a plurality of nozzles 36 within an orifice plate 38. The fluid-ejecting substrate is fluidically coupled to a reservoir of ink ((either within the cartridge, shown generally at 40, or externally (not shown)). Contact pads 42 carry electrical signals from a microprocessor in the printer to the IC in the die of the printhead to send signals, in the form of current, to specific resistors (not shown) associated with the nozzles 36, typically one nozzle per resistor. The control of specific resistors forms droplets of ink 44 that are ejected through the nozzles 36 onto print media, such as paper. The resistors also heat the droplets such that they dry on contact or near contact on the print media.
The TAB circuit 30 comprises a flexible tape 46. The back-side of the tape 48 includes a plurality of conductive traces 50, which are commonly copper and highly-susceptible to corrosion. Substrate 52, which contains a plurality of the heater resistors, is mounted onto the back-side of tape 46. The substrate 52 is bonded and electrically connected to traces on the tape via electrodes, which would be beneath windows 54.
The interconnect or interconnect pads are sealed or encapsulated, such as enumerated at 56 in FIG. 11, to protect the integrity of the electrical connection. Thus, encapsulation is typically used over the interconnect pads. This forms an encapsulant bead 58, which is exemplified in FIG. 13. The encapsulant bead has a profile height of xe2x80x9chxe2x80x9d (in the range of 0.5 mm) that must be taken into account when positioning the fluid-ejecting substrate of the printhead relative to the print media.
Referring also to FIG. 27, it is desirable to have the print media be as physically close to the nozzles of the fluid-ejecting substrate as possible (also called pen to paper spacing or PPS), taking into account that the print media type will require some clearance for issues such as paper cockle, envelope seams, and the like, (which is also in the range of 0.5 mm). By eliminating unnecessary encapsulation or bead height, or other profile height within the printhead, the conventional distance between the printhead and print media of 1.0 mm can be reduced by as much as approximately 0.5 mm. This close tolerance is highly desired as print quality is enhanced when the distance between the fluid-ejecting substrate and the print media is reduced.
The present invention is directed to a method for electrically connecting a chip or die having active circuitry to a substrate, whether in semiconductor applications or in thermal inkjet printer applications, without the need for TAB as a bonding means between the die and substrate. Each die includes a front-side and a back-side. At least one through-hole is formed within the die between the front-side and the back-side. Each aperture is aligned with a conductive trace on the substrate. A conductive member is inserted through a corresponding through-hole from the back-side of the die. One end of the conductive member is electrically connected to its corresponding trace. The conductive member is inserted through the die such that other end of the conductive member is exposed at the front-side of the die to contact an interconnect pad that is electrically connected to the active circuitry of the die.
The back-side of the die is bonded and sealed to the substrate about the at least one conductive member. A sealant is applied to the interconnect pad to substantially hermetically seal the electrical connection between the active circuitry and the trace.